Messages in this thread | | | Date | Fri, 13 Nov 2020 15:34:36 +0800 | From | Feng Tang <> | Subject | Re: [LKP] Re: [mm/memcg] bd0b230fe1: will-it-scale.per_process_ops -22.7% regression |
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On Thu, Nov 12, 2020 at 03:16:54PM +0100, Michal Hocko wrote: > On Thu 12-11-20 20:28:44, Feng Tang wrote: > > Hi Michal, > > > > On Wed, Nov 04, 2020 at 09:15:46AM +0100, Michal Hocko wrote: > > > > > > Hi Michal, > > > > > > > > > > > > We used the default configure of cgroups, not sure what configuration you > > > > > > want, > > > > > > could you give me more details? and here is the cgroup info of will-it-scale > > > > > > process: > > > > > > > > > > > > $ cat /proc/3042/cgroup > > > > > > 12:hugetlb:/ > > > > > > 11:memory:/system.slice/lkp-bootstrap.service > > > > > > > > > > OK, this means that memory controler is enabled and in use. Btw. do you > > > > > get the original performance if you add one phony page_counter after the > > > > > union? > > > > > > > > > I add one phony page_counter after the union and re-test, the regression > > > > reduced to -1.2%. It looks like the regression caused by the data structure > > > > layout change. > > > > > > Thanks for double checking. Could you try to cache align the > > > page_counter struct? If that helps then we should figure which counters > > > acks against each other by adding the alignement between the respective > > > counters. > > > > We tried below patch to make the 'page_counter' aligned. > > > > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h > > index bab7e57..9efa6f7 100644 > > --- a/include/linux/page_counter.h > > +++ b/include/linux/page_counter.h > > @@ -26,7 +26,7 @@ struct page_counter { > > /* legacy */ > > unsigned long watermark; > > unsigned long failcnt; > > -}; > > +} ____cacheline_internodealigned_in_smp; > > > > and with it, the -22.7% peformance change turns to a small -1.7%, which > > confirms the performance bump is caused by the change to data alignment. > > > > After the patch, size of 'page_counter' increases from 104 bytes to 128 > > bytes, and the size of 'mem_cgroup' increases from 2880 bytes to 3008 > > bytes(with our kernel config). Another major data structure which > > contains 'page_counter' is 'hugetlb_cgroup', whose size will change > > from 912B to 1024B. > > > > Should we make these page_counters aligned to reduce cacheline conflict? > > I would rather focus on a more effective mem_cgroup layout. It is very > likely that we are just stumbling over two counters here. > > Could you try to add cache alignment of counters after memory and see > which one makes the difference? I do not expect memsw to be the one > because that one is used together with the main counter. But who knows > maybe the way it crosses the cache line has the exact effect. Hard to > tell without other numbers.
I added some alignments change around the 'memsw', but neither of them can restore the -22.7%. Following are some log showing how the alignments are:
tl: memcg=0x7cd1000 memory=0x7cd10d0 memsw=0x7cd1140 kmem=0x7cd11b0 tcpmem=0x7cd1220 t2: memcg=0x7cd0000 memory=0x7cd00d0 memsw=0x7cd0140 kmem=0x7cd01c0 tcpmem=0x7cd0230
So both of the 'memsw' are aligned, but t2's 'kmem' is aligned while t1's is not.
I will check more on the perf data about detailed hotspots.
Thanks, Feng
> Btw. it would be great to see what the effect is on cgroup v2 as well. > > Thanks for pursuing this! > -- > Michal Hocko > SUSE Labs
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